1. Technical Field of the Invention
The present invention relates generally to an electromagnetic switch which is equipped with a built-in electronic control circuit and to be installed in a starter to start an automotive engine.
2. Background Art
Japanese Patent First Publication No. 9-105372 discloses an electromagnetic switch equipped with a built-in electronic control circuit to control energization of an exciting coil.
The electromagnetic switch is designed to use attraction, as produced by an electromagnet developed by the exciting coil, to open or close main contacts of a motor circuit. The electronic control circuit is disposed inside a contact cover in which the main contacts are installed. This structure is small in size as compared with the case where the electronic control circuit is disposed in a casing separate from the electromagnetic switch in electric connection therewith and thus facilitates installation of the electromagnetic switch in an engine compartment of the automobile. The structure also eliminates the need for cables and connectors for connecting the electromagnetic switch and the electronic control circuit electrically.
Within the contact cover, the main contacts (i.e., fixed and movable contacts) are disposed, thus causing arcs, as produced upon opening or closing of the main contacts, to melt and blow the material of the main contacts as conductive dusts. The electronic control circuit is, therefore, exposed to the dusts, so that the dusts are deposited on the surface of the electronic control circuit, which may result in a decrease in electric insulation between electric devices mounted on the electronic control circuit and short-circuits therebetween.
Therefore, the installation of the electronic control circuit within the contact cover requires a circuit board and conductive leads connecting with the circuit board to be blocked or shielded by an electric insulator, which will result in increases in volume and manufacturing cost of the electromagnetic switch.
It is also necessary to place the electronic control circuit within the contact cover away from a path along which the movable contact is to move in an axial direction of the contact cover, which may result in complex configuration of the circuit board and complex layout of the electric devices on the circuit board, thus leading to a decrease in ease of installation of the electronic control circuit.